MdeModulePkg: Add new API HttpUrlGetPath() to HttpLib.h

MdeModulePkg: Add new API HttpUrlGetPath() to HttpLib.h

This patch is to add a new interface to get the "Path" component according to
the URI parse result, it would be helpful for the library user to extract the
file path value in a URI.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>